A hydrodynamic fluid film bearing is known in the art, which is typically used to support a rotor shaft in a turbo or rotary machine such as a compressor, a blower, a motor, a generator, and other rotary apparatus or the like. Contrary to a conventional ball bearing or a journal bearing for supporting a rotor shaft, which typically uses an oil film as a lubricant and cooling medium for the rotor, the hydrodynamic fluid film bearing for a rotor shaft utilizes a high pressure air layer between the bearing and the rotor shaft. The hydrodynamic fluid film bearing is effective to support a rotor in particular for a small sized and light weighted turbo apparatus, which rotates at a high speed of 50,000 RPM to 150,000 RPM, for example.
FIG. 1 is a sectional view of one example of a conventional hydrodynamic fluid film bearing for supporting a rotor with an air layer formed between the bearing and the rotor for cooling heat generated in the apparatus.
Referring to FIG. 1, the hydrodynamic fluid film bearing of this type has a sleeve shape, and a rotation shaft 1 is received in a hollow inner space of the hydrodynamic fluid film bearing. When the rotation shaft 1 rotates, a gap G of typically 3 to 10 μm is formed between a bearing sleeve 20 and the rotation shaft 1. Because the rotation shaft 1 rotates in high speed with the fine gap G formed between the bearing sleeve 20 and the rotation shaft 1, a large amount of heat generated between the bearing sleeve 20 and the rotation shaft 1 cannot effectively be discharged from the apparatus.
To address this concern, various attempts have been made in which compressed air is forced into the gap G between the bearing sleeve 20 and the rotation shaft 1 for passing through the gap G in order to dissipate the heat. However, the compressed air circulating through the fine gap G cannot often effectively dissipate the overheating caused by high speed rotation of the rotation apparatus.
FIG. 2 is a sectional view of another example of a known hydrodynamic fluid film bearing. Referring to FIG. 2, hydrodynamic fluid film bearing 10 includes a sleeve 11 having a circular inner cavity 12 in which a rotation shaft 1 is rotatably received, and elastic metal foils 21 arranged at the hollow cavity 12 between the sleeve 11 and the rotation shaft 1.
The elastic metal foils 21 are arranged on the inner wall surface of the sleeve 11 typically partially overlapping one another. In this manner, one end of each metal foil 21 is fixed to an inner surface 11a of the sleeve 11 and the other end, which overlaps with an adjacent metal foil 21, generally contacts with the outer surface of the rotation shaft 1. As shown in the figure, the metal foil 21 can be fixed to the sleeve 11 with one end of the metal foil 21 inserted in a slot 13 formed on the inner surface 11a of the sleeve 11 and fixed with a fixing member 22 in the slot 13.
When the rotation shaft 1 rotates in the hollow opening 12 of the sleeve 11 at a certain speed, an air layer of high pressure is formed between the rotation shaft 1 and the metal foils 21. The rotation shaft 1 floats in the air due to the air pressure and rotates while maintaining a uniform distance from inner surface of the sleeve 11. Here, the metal foils 21 operate typically as a damper in supporting the rotation shaft 1.
However, if the rotation shaft 1 vibrates or trembles severely due to an external impact, for example, the rotation shaft 1 may be pushed against the metal foils 21 of the sleeve 11, causing damages to the sleeve 11 and the foils 21.
In order to solve such a problem, the metal foils may be overlapped one another to form multi-layered metal foils. However, such metal foils are typically not effective to provide adequate damping properties or supports to the rotation shaft in the presence of severe external impacts.